1. Field of the Invention
The present invention relates to a filter apparatus for use with a water tank which may be used to breed aquarium fishes, and more particularly relates to a filter apparatus of a type which can be secured to an upper edge of a water tank and is designed to pump up the water in the tank into a filtering chamber, so that the tank water is filtered by a filter element disposed in the chamber before returning into the water tank.
2. Description of the Prior Art
The prior art filter apparatuses for use with the water tanks for breeding aquarium fishes may be classified into two different groups, according to their positions with respect to the water tanks. In one of the groups, the filter apparatuses are placed under water, while in the other group they are disposed outside the water tank. In the latter case, the filter apparatus may be hung on the water tank wall, or alternatively rest on the upper edge thereof. Those apparatuses for external filtration is advantageous in that they can be employed irrespective of the dimension of water tank. Further, maintenance work such as replacement of filter elements is so easy that the external filtration apparatuses are preferred in this field.
Basically, the filter apparatuses of this type are of such a structure as disclosed in the U.S. Pat. No. 4,512,885. Such an apparatus generally comprises a box-like filtering chamber disposed outside and attached to the water tank peripheral wall, as well as a pump unit for pumping up the water of tank into the filtering chamber, and a filter element which is set transversely of the water passageway formed in the chamber. The filtered water which is cleaned and refreshed by the element will overflow out of the chamber, through a return canal and into the water tank.
It is however noted that the water in the prior art apparatuses is driven through the filter element predominantly by gravitational force imparted to the water itself. Therefore, the water will advance not uniform but locally through the filter element. This tendency becomes more and more remarkable as the dirt and impurities are caught by the element in course of time.
Such a preferential flow of the water through the element portion where flow resistance is lower than the remaining portions will lower the filtering efficiency, thus failing to filter the tank water to a sufficient extent. Durability of the filter element is also impaired, and it must be replaced with a new one in a relatively short time.